Researchers examined brain and heartMRI data on 1,504 patients without a history of neurologic disease enrolled in the Framingham Offspring Cohort study.

The participants, all between 34 and 84 years of age, half of whom were women, were divided into three groups based on the pumping ability (“cardiac index”) of their hearts. Participants whose hearts pumped the least amount of blood showed almost two years more brain aging than those with the healthiest hearts, researchers say.

People in the middle of the heart assessment group, who had low but still normal cardiac index levels, also showed lower brain volumes than people with the healthiest hearts.

Blood Flow and the Brain

As the brain ages, it starts to shrink or “atrophy,” and the decrease in volume is considered a sign of brain aging, the researchers say in a news release. More severe brain atrophy occurs in people with dementia, such as Alzheimer’s disease.

“These results are interesting in that they suggest cardiac index and brain health are related,” Angela L. Jefferson, PhD, study author and associate professor of neurology at Boston University School of Medicine, says in the news release.

“We expected an association between the lowest levels of cardiac index and smaller brain volumes, but we were surprised to find people on the lower end of normal cardiac index also have smaller brain volumes when compared to people with very healthy cardiac index,” Jefferson says.

Because only 7% of patients had heart disease, Jefferson and colleagues say they did not expect that 30% of people in the study would have relatively low heart pumping function.“These participants are not sick people,” she says. “A very small number have heart disease. The observation that nearly a third of the entire sample has low cardiac index and that lower cardiac index is related to smaller brain volume is concerning and requires further study.”

Patients with smaller brain volumes did not show obvious signs of diminished brain function, the researchers say. “We observed cardiac index is related to structural changes in the brain but not cognitive changes,” Jefferson says. “The structural changes may be early evidence that something is wrong.” Those people will continue to be studied to see how structural brain changes affect memory and cognitive abilities in the future.

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Heart Health, Brain Health Linked?

Jefferson says the exact cause for a link between heart function and brain volume is not well understood. “There are several theories for why reduced cardiac index might affect brain health,” she says. “For instance, a lower volume of blood pumping from the heart might reduce blood flow to the brain, providing less oxygen and fewer nutrients needed for brain cells.”

She says it’s too early to offer advice based on the study, “but it does suggest that heart and brain health go hand in hand.”

The apparent impact on the brain was stronger for people below age 60, which, the authors write, “coincides with a period in the lifespan with reduced risk for abnormal brain changes, possibly allowing the influence of cardiac index on brain health to be more prominent.”

In an accompanying editorial, Clinton B. Wright, MD, and Ralph L. Sacco, MD, of the University of Miami Miller School of Medicine, write that a better understanding of links between cardiovascular disease and brain structure and function is needed “to identify early markers of unsuccessful aging to test interventions that can improve outcomes.”

The study and editorial are published in the August issue of Circulation: Journal of the American Heart Association.